//C08:Mutable.cpp -- The "mubable" keyboard
class Z
{
    int i;
    mutable int j;
    public:
        Z();
        void f() const;
};

Z::Z(): i(0), j(0) {}

void Z::f() const
{//! i++; // Error --const member function
    j++;   // OK: mutable
}

int main(void)
{
    const Z zz;
    zz.f(); // Actually change it!
}